Small portable wireless communication devices typically include a single stub, patch, or L-shaped antenna to receive/transmit over a wireless communications link to the device. While such antenna arrangements generally work well, there remains dead or weak spots which require the user to change position or move to obtain better reception/transmission. This is particularly true for devices such as a Personal Digital Assistance (PDA) which use a patch antenna which is usually placed on the back of the PDA. Such PDAs often must be oriented with the back facing the general direction of the base station to obtain good reception.
Unfortunately, because of the small dimensions of these wireless communication devices, there is typically no way to add a second antenna to provide antenna diversity. Thus there is a continuing need to improve the performance of these wireless communication devices.
The present invention describes a technique for placing more than one antenna on a wireless expandable terminal which is extended during use. In accordance with the present invention, a second antenna is placed in a moveable section that extends away from the main body of the device, in the extended position the second antenna is located at a spacing which is half a carrier wavelength from the main antenna. The second antenna can be a fixed or a retractable antenna.
The use of multiple antennas on a wireless terminal has been described in the prior art, for example see U.S. Pat. No. 5,337,061 entitled "High Performance Antenna for Hand-Held and Portable Equipment" issued to M. R. Pye et al on Aug. 9, 1994. In that patent the terminal is provided with two antennas which are not used for antenna diversity purposes, but rather the second antenna is switchably substituted for a first antenna when the performance of that first antenna is degraded due to its proximity to the user's head or other obstacle. Since the two antennas, are not necessarily located one half wavelength apart they do not provide the antenna diversity of our invention. Additionally, the Pye patent switches between the two antennas rather than combining both antenna signals as in our invention.